1. Field of the Invention
The present invention relates to a modified carbon black, a process for producing the modified carbon black, a rubber composition and a pneumatic tire. More particularly, the present invention relates to a novel carbon black modified at the surface and a rubber composition and a pneumatic tire comprised of the modified carbon black and exhibit a remarkably improved gripping property.
2. Description of the Related Arts
As the automobile industry makes progress, automobiles are having higher power and exhibiting higher performances. At the same time, safety is considered more important and more improvement in the gripping property of a tire is required.
Heretofore, as the method for improving the gripping property of a tire, it is known that carbon black having a relatively large specific surface area such as an SAF black can be used for increasing hysteresis loss of a tread rubber. It is also known that, in combination with the above carbon black, a large amount of an oil having a high content of aromatic components can be used or a styrene-butadiene copolymer rubber containing a relatively large amount of bound styrene can be used. However, the use of carbon black having a large specific surface area causes a poor dispersion of the carbon black into rubber. The use of an increased amount of oil or carbon black to improve the gripping property causes a problem in that the surface of a tread becomes rough after being abraded.
In Japanese Patent Application Laid-Open No. Heisei 7(1995)-118452, a tread rubber composition comprising a silylating agent to improve gripping property on a frozen road surface is described. However, when a silylating agent is simply added to a rubber composition, unreacted silylating agent in the rubber composition adversely affects physical properties of the vulcanized rubber composition such as fracture resistance, and improvement in the gripping property is insufficient.
The present invention has been made to overcome the limitation in the conventional technology described above and has an object of providing a rubber composition exhibiting remarkably improved high hysteresis loss property, a modified carbon black advantageously used for the rubber composition and a process for producing the modified carbon black. The present invention has another object of providing a pneumatic tire which exhibits a remarkably improved gripping property due to the above rubber composition used for a tread rubber.
As the result of extensive studies by the present inventors to overcome the above problems with an attention focussed on carbon black, it was found that a carbon black, in which chemically active sites containing an oxygen atom such as hydroxyl group at the surface are inactivated by the treatment with a specific compound to form a specific chemical structure at the surface, can be effectively used. The present invention has been completed based on this knowledge.
The present invention provides:
(1) A rubber composition which comprises a rubber component comprising at least one rubber selected from the group consisting of natural rubber and synthetic diene rubbers and, per 100 parts by weight of the rubber component, 30 to 200 parts by weight of a modified carbon black at its surface, an Sixe2x80x94Oxe2x80x94C structure or an Sixe2x80x94C structure in which the carbon atom bonded directly to the Si atom is an aromatic carbon atom;
(2) A rubber composition which comprises a rubber component comprising at least one rubber selected from the group consisting of natural rubber and synthetic diene rubbers and, per 100 parts by weight of the rubber component, 30 to 200 parts by weight of a modified carbon black which obtained by bringing carbon black, in a gas phase, into contact with at least one compound selected from the group consisting of silicon compounds represented by the general formula (I):
(R1O)mSiR24xe2x88x92mxe2x80x83xe2x80x83(I)
wherein R1 represents an alkyl group having 1 to 3 carbon atoms, R2 represents an alkyl group having 1 to 3 carbon atoms or a phenyl group and m represents an integer of 2 to 4;
(3) A rubber composition which comprises a rubber component comprising at least one rubber selected from the group consisting of natural rubber and synthetic diene rubbers and, per 100 parts by weight of the rubber component, 30 to 200 parts by weight of a modified carbon black which is obtained by bringing carbon black, in a gas phase, into contact with at least one compound selected from the group consisting of silicon compounds represented by general formula (II):
(R3O)nSiR44xe2x88x92nxe2x80x83xe2x80x83(II)
wherein R3 represents an alkyl group having 1 to 3 carbon atoms, R4 represents an alkyl group having 1 to 3 carbon atoms, a phenyl group or phenoxy group, at least one of groups represented by R4 being a phenyl group or a phenoxy group, and n represents an integer of 1 to 3;
(4) A pneumatic tire prepared by using a rubber composition described in any of (1) to (3); and
(5) A process for producing a modified carbon black which comprises bringing carbon black into contact with at least one compound selected from the group consisting of silicon compounds represented by the above described general formula (I) and silicon compounds represented by the above described general formula (II) in a gas phase.